Quasi-triple bonds and ultrashort Be–Be distances in binary superhalogen clusters [X–Be2(BeX)3–X]− (X = Cl, Br, I)

Abstract

In computational design, clusters with minimal elemental composition are prioritized for superior gas-phase synthetic accessibility, yet most reported main-group metal clusters exhibiting ultrashort metal–metal distances (USMDs, dM–M < 1.900 Å) require complex ternary or quaternary systems, severely limiting experimental realization. We demonstrate that binary superhalogen clusters [X–Be2(BeX)3–X]− (X = Cl, Br, l) achieve the desired USMD via formation of a quasi-triple bond composed of three 3c–2e bonds between two axial beryllium atoms, resulting in compressed Be–Be distances ranging from 1.832 to 1.851 Å. Their exceptional superhalogen characteristics result from vertical detachment energies (VDEs) of 4.65–4.70 eV, surpassing the threshold (VDE = 3.62 eV) by over 1.00 eV and indicating good stability. Consistently, [X–Be2(BeX)3–X]− (X = Cl, Br, l) are identified as dynamically stable global energy minima exhibiting wide HOMO–LUMO gaps (6.38–6.62 eV), which establish them as promising candidates for experimental validation of USMDs between main-group metals.